Agriculture and Farm Equipment
Agriculture and Farm Equipment Repair Questions? Ask a Mechanic.
What kind of gear case oil are they running? You may need to run a thinner oil being underground.
Have you tries an oil additive in a new gear case? Maybe lucas oil additive would help with the gear case over heating problem.
I would try some of this into a gear case and see if it helps http://lucasoil.com/products/engine-oil-additives/heavy-duty-oil-stabilizer
Have you checked the bearings to see if they are locked up?
Any update on you gear case problem?